Science Questions

The following preliminary list of science questions have been developed for guiding the field research of CalNex 2010. They are intended to be 1) feasible to address in the context of the proposed study 2) specific enough to provide a needed focus, but 3) general enough to cover the scientific issues of immediate policy interest. They will be revised as needed to form the basis of the Science Plans that will be developed by the participating agencies. These questions fall into three broad categories.

Emissions

How can we improve the emissions inventory for greenhouse gases, ozone and aerosol precursors including emissions from soil, ships, agriculture and other non-industrial or transportation related processes? What measurements can help validate the use of satellite data for biogenic VOC and NOx emission inventories?

What emissions (natural and anthropogenic) and processes lead to sulfate formation over California coastal waters and in urbanized coastal areas? What is the contribution from ship emissions? How does Southern California compare and contrast with the San Francisco Bay Area?

What sources and processes contribute to atmospheric mercury concentrations in California?

Critical uncertainties remain in our understanding of 1) the processes by which primary emissions are transformed within and removed from the atmosphere, and 2) how aerosols interact with the radiation flux in the atmosphere.

Chemical Transformation and Climate Processes

How important are chemical processes occurring at night in determining transport and / or loss of nitrogen oxides, reactive VOC and ozone? Do regional models in California adequately represent these processes and their effect on air quality?

What are the sources and physical mechanisms that contribute to high ozone concentrations aloft that have been observed in Central and Southern California?

Are there significant differences between Central Valley and South Coast Air Basin precursors or ozone formation chemistry? Will meteorological and/or precursor differences between the Central Valley and the South Coast Air Basin lead to different chemical transformation processes and different responses to emissions reductions? What is the importance of natural emissions to the ozone formation process? Are there regional differences in the formation rates and efficiency for particulate matter as well?

What are the impacts of aerosols in California on radiative forcing and cloud formation? What are the most important precursors and formation processes for secondary organic aerosol? What is the role of aqueous phase processes in atmospheric transformations?

Climate change and air quality problems have both global and regional scale aspects that interact through atmospheric transport. Critical uncertainties remain in our understanding of these interactions.

Transport and Meteorology

What are proper oceanic boundary conditions for coastal and regional atmospheric chemistry modeling? Are there variations in oceanic boundary conditions in northern and central California vs. the southern part of the state? What physical and chemical changes occur as a parcel of air moves from off-shore, through the shore zone, and inland?

How best can we characterize and model air flow over coastal waters and the complex terrain of California? For example: what is the best representation of air flow in the southern San Joaquin Valley, particularly with respect to flow between the San Joaquin Valley and South Coast Air Basin versus recirculation north along the Sierra Nevada and Coastal ranges?

What are the major deficiencies in the representation of chemistry and meteorology in research and operational models and how can models be improved through the collection of additional measurements? What physical and chemical processes are not captured well by available models? Is there an optimum grid resolution to capture all of the relevant physical and chemical processes that occur?

What are the important transport corridors for key chemical species and under what conditions is that transport important?

What is the relative roles of regional (North American) sources and long range transport (from East Asia) on aerosol forcing over California?

It is expected that CalNex 2010 will be able to address each of the science questions listed above, although with differing degrees of emphasis. Prioritization of topics will occur during planning and execution of the study. The instruments that can be deployed on the various platforms and surface sites, and for how long they can be deployed, will be determined when there is clear understanding regarding the resources available for CalNex 2010. During the field study, the day-to-day deployment of the mobile platforms will determine the emphasis on particular questions.